The present invention relates to an apparatus for the photocatalytic treatment of a fluid, and to a method for treating a fluid using such an apparatus.
Photochemical reactions which can be carried out in an apparatus which exposes a fluid containing one or more contaminants to high-energy radiation are known. Such reactions include photocatalytic mineralization of toxic chemicals in water and photocatalytic oxidation of metals in water, and typically involve the use of a powdered photocatalyst, which can be a semiconductor material such as TiO.sub.2. These reactions are described, for example, in U.S. Pat. Nos. 4,264,421; 4,303,486; 4,774,026; 4,861,484; 4,888,101; 4,892,712; 4,943,357; 4,954,465; 4,997,576; 5,035,784; 5,045,288; 5,137,607; and 5,182,030; European Published Application No. EP 0 306 301 A1; European Application No. 90201172.5; and PCT Applications No. WO 91/09823 and WO 91/04094, the contents of each of which are incorporated in their entireties by reference.
It is known to conduct photocatalytic reactions in small-scale laboratory vessels, and in reactors such as conventional "pot" reactors wherein a source of ultraviolet radiation, such as a lamp, illuminates a reaction mixture comprising a contaminated fluid and a catalyst system within a stirred-tank reactor. Other types of apparatus for carrying out such reactions are known, for example, from U.S. Pat. Nos. 5,137,607; 5,035,784; and 4,888,101.
Certain known types of reactors include dedicated means for exposing a photocatalyst and fluid flowing therein to ultraviolet radiation. Such means can include, for example, one or more lengths of piping that are transmissive in at least some sections to ultraviolet radiation. The fluid can contain suspended therein the photocatalyst (usually in finely powdered form, having a particle diameter on the order of 20-300 .mu.m). In an alternative, the exposing means can contain therein a granular material having a coating which includes the photocatalyst. That is, the exposing means can have a "packed bed" configuration.
However, the known photocatalytic reactors have proven impractical for the treatment of contaminated fluids on an industrial scale and/or in an outdoor environment. In particular, known ultraviolet-transmitting materials have drawbacks which preclude their effective commercial use in photocatalytic reactors. For example, borosilicate glass lacks adequate impact resistance and shear resistance. Thus, photocatalytic reactors employing borosilicate glass are easily damaged by adverse environmental conditions, such as hailstorms. Quartz is very expensive and thus not commercially practical. Fluorinated hydrocarbon plastics, such as those available under the tradenames Kynar and Teflon, are ultraviolet-transmissive if they are of low thickness, but in such form they are not self-supporting or capable of withstanding pressurization. On the other hand, when these plastics have sufficient thickness to be self-supporting and pressurizable, they lack the requisite ultraviolet transmissivity.
Thus it becomes important to provide an apparatus which enables the photocatalytic treatment of a fluid to be carried out easily and effectively. It likewise becomes important to provide a method of treating a fluid using such an improved apparatus.